feat(cityenergy_l10wfe_gaswaterheater): add fault sensor, optional meter resets (#5302)

* feat(cityenergy_l10wfe_gaswaterheater): add fault sensor, optional meter resets

Enhance the existing City Energy L10WFE gas water heater config (#4921):

- Add a 'problem' binary_sensor exposing fault state and raw fault code (dp 20),
  following the established sensor + fault_code bitfield pattern.
- Mark the reset water/gas meter buttons (dp 107/108) as optional, since not all
  units report these dps; improves matching reliability.

Verified against a City Energy L10WFE (product id di9ybnrv3s2d1axk).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Remove explicit name to allow translations to be used

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-authored-by: Jason Rumney <make-all@users.noreply.github.com>

custom_components/tuya_local/devices/cityenergy_l10wfe_gaswaterheater.yaml

@@ -102,6 +102,7 @@ entities:
     dps:
       - id: 107
         type: boolean
+        optional: true
         name: button
   - entity: button
     name: Reset gas meter
@@ -110,4 +111,19 @@ entities:
     dps:
       - id: 108
         type: boolean
+        optional: true
         name: button
+  - entity: binary_sensor
+    class: problem
+    category: diagnostic
+    dps:
+      - id: 20
+        type: bitfield
+        name: sensor
+        mapping:
+          - dps_val: 0
+            value: false
+          - value: true
+      - id: 20
+        type: bitfield
+        name: fault_code